Today I tried to get my applet on a website and noticed that I had to sign it. After signing it now I'm troubled with this. Can I do anything to prevent this for FREE (as I'm underage and I can't really pay anyone anything)

No, there is nothing you as a developer can do about the security popup. It's an integral part of Java's security model and it will appear no matter who the signer of the applet is. The end user has the option to disable it for trusted signers/publishers (the option to do so should be under the "more options" on the popup), but since it's their hardware your code is executing on, they have the final word in the matter, not you.

Arthur: Are all men from the future loud-mouthed braggarts?Ash: Nope. Just me baby...Just me.

Maybe I'm missing something here, but that article is directed at end users, the ones who have the ability to run or block your applet, not developers. While there are different types of warning messages depending on the level of trust, even code from a "trusted authority" still triggers a security dialog with warnings about risk to personal information.

As stated before, there is nothing that you as a developer can do to prevent a security warning.

Arthur: Are all men from the future loud-mouthed braggarts?Ash: Nope. Just me baby...Just me.

Either offer an executable jar, a bundled exe(For windows convenience) or if you are really deadset on the web. LibGDX offers a great html5 publishing ability.

There are other ways to port to html, and a lot of times it works fairly well. Or possibly even a JNLP I think would be better?

I used to spend a lot of time trying to get applets to work, then I realized its not worth it, for dozens of reasons. Especially now with more browsers throwing more warnings about it. The mountain is even steeper.

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